The present invention relates to liposomal formulations of certain antisense oligonucleotides, specifically liposomal phosphodiester, phosphorothioate, and p-ethoxy oligonucleotides. The invention also relates to methods of making such formulations and methods of using such formulations in medical therapy.
Antisense oligonucleotides (oligos), complementary to specific regions of the target mRNA, have been used to inhibit the expression of endogenous genes. When the antisense oligonucleotides bind to the target mRNA, a DNA-RNA hybrid is formed. This hybrid formation inhibits the translation of the mRNA and, thus, the gene's expression of the protein. If the protein is essential for the survival of the cell, the inhibition of its expression may lead to cell death. Therefore, antisense oligonucleotides can be useful tools in anticancer and antiviral therapies.
The main obstacles in using antisense oligonucleotides to inhibit gene expression are cellular instability, low cellular uptake, and poor intracellular delivery. Natural phosphodiesters are not resistant to nuclease hydrolysis; thus high concentrations of antisense oligonucleotides are needed before any inhibitory effect is observed. Modified phosphodiester analogs, such as phosphorothioates, have been made to overcome this nuclease hydrolysis problem, but they have not provided a completely satisfactory solution to the problem.
The cellular uptake of antisense oligonucleotides is low. To solve this problem, physical techniques such as calcium-phosphate precipitation, DEAE-dextran mediation, or electroporation have been used to increase the cellular uptake of oligonucleotides. These techniques are difficult to reproduce and are inapplicable in vivo. Cationic lipids, such as Lipofectin, have also been used to deliver phosphodiester or phosphorothioate oligonucleotides. An electrostatic interaction is formed between the cationic lipids and the negatively charged phosphodiester or phosphorothioate oligonucleotides, which results in a complex that is then taken up by the target cells. Since these cationic lipids do not protect the oligonucleotides from nuclease digestion, they are only useful in delivering the nuclease-resistant phosphorothioates, but not the nuclease-cleavable phosphodiesters.
Another modified phosphodiester (PD) analog that has been prepared is p-ethoxy (pE) oligos. The modifications of pE oligos are made in the phosphate backbone so that the modification will not interfere with the binding of these oligos to the target mRNA. pE oligos are made by adding an ethyl group to the nonbridging oxygen atom of the phosphate backbone, thus rendering these oligos uncharged compounds. In spite of their resistance to nucleases, the cellular uptake and intracellular delivery of pE oligos are still poor because upon internalization, these oligos remain sequestered inside the endosomal/lysosomal vacuoles, impeding their access to the target mRNA.
There is a need for improved antisense compositions for use in treatment of disease, and also a need for processes for making such improved compositions.